Predator Prey Interactions That Affect Survival Of Migrant Sockeye Salmon Oncorhynchus Nerka Fry PDF Download

Adult Pacific salmon arrive at the Fraser River with a finite supply of energy to allocate between reproductive development and river migration, yet it is unknown if environmental conditions experienced by parents cause energetic trade-offs that ultimately affect offspring fitness. This thesis examined populations of Fraser River sockeye salmon (Oncorhynchus nerka) that differed in their mirgration distance (Weaver - 100 km, Gates - 363 km, and Early Stuart - 1086 km) to assess the hypothesis that migratory stress exerts an intergenerational effect on offspring fitness. When compared among three year classes of Early Stuart sockeye salmon, metrics for ovarian development at six locations along the migration route revealed no evidence of facultative adjustments of either egg number or egg size en route. In contrast, significant interannual variation existed for final ovary mass, egg size and egg number over a 16-year period, with reductions in ovary mass and egg size associated with years of high river discharge rate during the migration. Selection against maternal phenotypes with a high ovarian investment strategy was postulated as a mechanism to reconcile both data sets. Maternal and paternal gamete origin significantly influenced offspring survival. However, egg viability did not correlate with phenotypic variation in maternal energetic condition, osmoregulatory status, reproductive hormonal state, egg composition, stress, or moribund condition. Nevertheless, at the population level, migration severity may have impacted overall egg quality because (a) the two populations that experienced more severe migration conditions in 1999 and 2000 had the lowest overall embryo survival (Gates = 77%; Early Stuart = 81%; Weaver = 94%; - artifical fertilizations), and (b) a poor maternal condition (using pre-spawn mortality as surrogate of poor condition and adverse migration conditions) was positively correlated with low egg to fry survival in Early Stuart sockeye salmon over a 15 year period. Given that changes in egg size and the number of surviving offspring associated with parental influences are clear examples of intergenerational effects in sockeye salmon, the weight of evidence suggests that migratory stress associated with the parental spawning migration can contribute to an alteration in intergenerational gene flow and offspring size.